This invention relates to disposable medical blood pressure measuring devices that are utilized with in vivo catheters to measure and record the blood pressure of a patient. Basically, in vivo blood pressure monitoring is widely used in hospitals and includes a liquid filled catheter system that is introduced into the particular blood vessel to be monitored. The open end of the liquid filled catheter thus is placed within the patient's blood vessel and a continuous column of liquid takes up the space between that catheter end and a pressure transducer. The blood pressure may therefore be directly measured by the transducer remote from the patient by measuring the fluctuations of pressure at the external end of the liquid column.
Typically, such pressure transducers comprise strain guages in the form of cantilever beams, for example in U.S. Pat. No. 4,545,389 and 4,683,894, or may comprise tiny silicon chips with a moveable diaphragm etched into the chip. One side of the diaphragm or cantelever beam is subject to the fluctuating pressures transmitted by the column of liquid while the other side is vented to atmosphere. The transducer then electronically senses the amount of flexing of the diaphragm or chip and translates the amount of flex into an electrical signal.
It is, obviously, of extreme importance that the column of liquid filling the tubing and catheter between the pressure transducer and the open end of the catheter be solid, that is, free of air or other gas bubbles.
Any such air bubbles in the liquid column creates frequency degrading, erroneous pressure waveforms and/or misleading diastolic and systolic pressure measurements. Certainly, in the hospital environment, and particularly, due to the major use of invivo blood pressure sensing in the operating room, or cath lab, accuracy and fidelity of signal is of extreme importance.
In setting up such invivo blood pressure systems, it is standard to flush the system, including the patient side of the pressure transducer with a sterile liquid to insure that the transducer is completely filled with liquid. A syringe connected to a stopcock located at one end of the transducer normally is used to force liquid through the stopcock and into a passageway passing through the transducer and out a downstream opening on the opposite side of the transducer. The preferred stopcock is a two position valve alternating between one position where the syringe communicates with the transducer passageway and another position when the line containing the column of liquid to the patient communicates with the transducer passageway. When sufficient liquid has been flushed out the downstream opening, a cap, known as a deadender cap is tightened to close the downstream opening of the transducer. The stopcock is then moved to its position that shuts off the communication with the syringe and opens the patient line to the transducer.
In many such pressure transducers, the downstream opening is a standard male Luer lock fitting, which conforms to certain medical uniform specifications and which ends in a fairly flat, circular opening.
In present deadender caps, a flat surface is formed in the closed end of the caps. One disadvantage of such deadender caps has been discovered to be the trapping of minute to large amounts of air as they are closed tight by engagement of the threaded lock. The air is trapped by engagement of the Luer tapers or in moving the flat surface into abutment with the circular opening to deadend the downstream opening. A recurring problem has thus arisen in that a bubble is created and which readily enters the transducer itself since, in use, the transducer may often be inverted or moved into various positions that would induce a bubble to progress along the liquid filled transducer passageways causing the aforedescribed difficulties in the transducer use and accuracy.